GLOBAL PATTERNS OF INSOLATION RECEIPTS

The following image describes the annual pattern of solar radiation absorption at the Earth's surface for the year 1987.

Figure 7g-1: Annual (1987) pattern of solar radiation absorbed at the Earth's surface.

(Image created by the CoVis Greenhouse Effect Visualizer).

The combined effect of Earth-Sun relationships (angle of incidence and day length variations) and the modification of the solar beam as it passes through the atmosphere produces specific global patterns of annual insolation receipt as seen on Figure 7g-1 above (and see the NASA WWW links below). After examining these patterns, the following trends can be identified:

• Highest values of insolation received occur in tropical latitudes. Within this zone there are localized maximums over the tropical oceans and deserts where the atmosphere has virtually no cloud development for most of the year. Insolation quantities at the equator over land during the solstices are approximately the same as values found in the middle latitudes during their summer (seeNASA WWW links below).
• Outside the tropics, annual receipts of solar radiation generally decrease with increasing latitude. Minimum values occur at the poles. This pattern is primarily the result of Earth-Sun geometric relationships and its effect on the duration and intensity of solar radiation received.
• In middle and high latitudes, insolation values over the ocean, as compared to those at the same latitude over the land, are generally higher (see NASA images). Greater cloudiness over land surfaces accounts for this variation.

NASA's Surface Radiation Budget Project has used satellite data, computer models, and meteorological data to determine shortwave surface radiation fluxes for the period July 1983 to June 1991.

Average Available Solar Insolation at the Earth's Surface: January 1984-1991 (K + k)

Figure 7g-2: Average available solar insolation at the Earth's surface: January 1984-1991. Highest values of available solar insolation occur at the South Pole due to high solar input and little cloud cover. High values also occur along the subtropical oceans of the Southern Hemisphere. Color range: blue - red - white, Values: 0 - 350 W/m2. Global mean = 187 W/m2, Minimum = 0 W/m2, Maximum = 426 W/m2. (Source: NASA Surface Radiation Budget Project).

Average Available Solar Insolation at the Earth's Surface: July 1983-1990  (K + k)

Figure 7g-3: Average available solar insolation at the Earth's surface: July 1983-1990. Highest values of available solar insolation over Greenland due to high solar input and low cloud amounts. High values also occur along the subtropics of the Northern Hemisphere. Color range: blue - red - white, Values: 0 - 350 W/m2. Global mean = 180 W/m2, Minimum = 0 W/m2, Maximum = 351 W/m2. (Source: NASA Surface Radiation Budget Project).

Average Absorbed Solar Insolation at the Earth's Surface: January 1984-1991 [(K + k)(1 - a)]

Figure 7g-4: Average absorbed solar insolation at the Earth's surface: January 1984-1991. Highest values occur along the subtropical oceans of the Southern Hemisphere. Lowest values occur over areas of high surface reflection such as the South Pole, cloudy regions, and areas of low solar input like the high latitudes of the Northern Hemisphere. Color range: blue - red - white, Values: 0 - 350W/m2. Global mean = 162 W/m2, Minimum = 0 W/m2, Maximum = 315 W/m2. (Source: NASASurface Radiation Budget Project).

Average Absorbed Solar Insolation at the Earth's Surface: July 1983-1990  [(K + k)(1 - a)]

Figure 7g-5: Average absorbed solar insolation at the Earth's surface: July 1983-1990. Highest values occur over the subtropical oceans of the Northern Hemisphere due to high solar input and little cloud coverage. Lowest values occur in areas of high surface reflection such as snow/ice covered surfaces like Greenland, cloudy regions such as storm tracks, and areas of low solar input like the high latitudes of the Southern Hemisphere. Color range: blue - red - white, Values: 0 - 350W/m2. Global mean = 158 W/m2, Minimum = 0 W/m2, Maximum = 323 W/m2. (Source: NASASurface Radiation Budget Project).

In the equations above, the mathematical terms have the following definitions 

K = Shortwave Direct Radiation

k = Shortwave Indirect Radiation

a = Reflectivity of the Surface or Surface Albedo

CITATION

Pidwirny, M. (2006). "Global Patterns of Insolation Receipts". Fundamentals of Physical Geography, 2nd Edition. 30/11/2011. http://www.physicalgeography.net/fundamentals/7g.html